Air conditioning systems include a mechanical compressor that compresses refrigerant flowing through the air conditioning system. The compressor requires oil to function properly and efficiently. During normal operation of the air conditioning system, a portion of the compressor oil is entrained in the refrigerant and circulated through the air conditioning system. When the air conditioning system is serviced, the refrigerant, along with the oil entrained therein, is typically removed from the air conditioning system. Additionally, the air conditioning system may require replacement of parts within the circuit, which can also remove compressor oil within the replaced parts. As such, new compressor oil must be injected into the system to replace oil removed from the system during maintenance and service operations. For this reason, most air conditioning service (“ACS”) machines include a circuit for injecting oil into the air conditioning circuit prior to recharging refrigerant into the air conditioning system.
Measuring the oil injected into the air conditioning system is important to ensure the proper quantity of compressor oil is in the air conditioning circuit. Excess or insufficient oil in the compressor reduces the overall operational efficiency of the air conditioning system. One commonly used method of measuring oil injected into the air conditioning system is visual identification. Some conventional ACS machines include a bottle of oil having graduated markings that indicate the amount of oil in the bottle. To measure the quantity of oil injected into the system, the user monitors the oil level in the bottle with reference to the graduated markings as the ACS machine injects the oil, and terminates the injection operation when the desired quantity of oil appears to have been injected. This method has the lowest cost, but relies entirely on the user to monitor the bottle and inject the correct amount. As a result, the visual identification method suffers from issues, including operator error and inaccuracy of the markings or in reading the markings that can cause deviation from the desired quantity of oil injected into the air conditioning system.
Some conventional ACS machines include a load cell associated with the oil bottle to measure the weight of the oil bottle. The system is configured with a controller that subtracts the weight of the bottle during the injection process from the initial weight of the bottle to determine the amount of oil injected. Once the controller determines that the desired quantity of oil has been injected into the system, the controller operates the oil injection valve to close. However, load cells are expensive and delicate, and, as a result, ACS machines having a load cell for the oil bottle are costly to manufacture and maintain, and may malfunction if handled incorrectly.
Other typical ACS machines estimate the quantity of oil injected into the air conditioning system based on the time the oil injection solenoid valve is open. The oil flow rate is assumed, and a length of time that the oil injection solenoid valve needs to be open in order to inject the desired quantity of oil is estimated from the assumed oil flow rate. For example, in some ACS machines, the oil flow rate is assumed to be 2 ml per second. A user inputs the amount of oil for the system to inject, for example 10 ml. The ACS controller then calculates the time the system should be open, which, in this example, is 5 seconds.
One issue with such an oil injection method is that the oil flow rate is not a constant. The flow rate varies depending on the oil viscosity and the temperature of the oil, which is typically approximately the ambient temperature of the ACS machine. Some ACS machines that include time-based oil injection also include a way for the user to input a correction factor to correct the injected quantity or the time the valve is open based on variations in the flow rate due to the current conditions. One problem with this is that the user may not have accurate information to determine the proper correction factor. Another issue is that the user may be required to perform baseline tests or calculations in order to determine the correction factor, and errors in these tests or calculations can result in an incorrect correction factor being input to the machine. As a result, the time injection method fails to provide adequate accuracy due to the required user intervention and system variables.
For all of the above reasons, it would be desirable to provide an ACS machine that improves the precision of the quantity of oil injected into an air conditioning system at a low cost. Additionally, it would be desirable to provide an ACS machine that accurately injects a desired quantity of oil into the air conditioning system with minimal user intervention.